Biomedical subjects
Publications and source records attributed to A Jacquier.
Management of high-flow arteriovenous malformation remain often problematic. Complete eradication of the nidus is the only potential cure, but this, however, is often difficult if not impossible. Frequently, a multidisciplinary approach is required. In these article, techniques and results of the endovascular management of MAV are discussed.
The reasons for the cellular specificity and slow progression of motoneuron diseases such as ALS are still poorly understood. We previously described a motoneuron-specific cell death pathway downstream of the Fas death receptor, in which synthesis of nitric oxide (NO) is an obligate step. Motoneurons from ALS model mice expressing mutant SOD1 showed increased susceptibility to exogenous NO as compared with controls. Here, we report a signaling mechanism whereby NO leads to death of mutant, but not control, motoneurons. Unexpectedly, exogenous NO triggers expression of Fas ligand (FasL) in cultured motoneurons. In mutant SOD1(G93A) and SOD1(G85R), but not in control motoneurons, this up-regulation results in activation of Fas, leading through Daxx to phosphorylation of p38 and further NO synthesis. This Fas/NO feedback amplification loop is required for motoneuron death in vitro. In vivo, mutant SOD1(G93A) and SOD1(G85R) mice show increased numbers of positive motoneurons and Daxx nuclear bodies weeks before disease onset. Moreover, FasL up-regulation is reduced in the presence of transgenic dominant-negative Daxx. We propose that chronic low-level activation of the Fas/NO feedback loop may underlie the motoneuron loss that characterizes familial ALS and may help to explain its slowly progressive nature.
The authors report the clinical and imaging features of a patient with rupture of an aortoiliac graft successfully treated by endovascular approach. The endovascular treatment is easy to perform and effective. The main pitfall of this technique is the limited availability of stent-grafts.
Arrhythmogenic right ventricular dysplasia (ARVD) is a cardiomyopathy of unknown etiology responsible for 20% of cases of sudden death in young adults secondary to arrhythmia. It is characterized histologically by fatty or fibro-fatty infiltration of the right ventricular myocardium. Diagnostic criteria have been proposed for diagnosing ARVD. Imaging, especially MRI, plays an important role. MR imaging must be performed using cardiac gating, and should include both cine-MR sequences for evaluation of segmental and global right ventricular function or any morphological change of the right ventricular shape, and anatomic sequences to detect fatty or fibro-fatty infiltration of the right ventricular myocardium.
CT, MRI and transesophageal echocardiography have become the standard of reference for evaluation of the thoracic aorta. Angiography is mainly performed as a presurgical procedure. Congenital pathologies observed during adulthood include coarctation, patent ductus arteriosus, and aberrant retroesophageal subclavian arteries. Imaging plays a major role for diagnosis and management of patients with acute aortic syndromes: intramural hematoma, dissection, penetrating ulcer and nondissecting aneurysms. Cross sectional imaging of the thoracic aortic wall allows evaluation of inflammatory diseases of the aorta or aortitis.
PURPOSE: To evaluate the ability of CT imaging to detect infectious lesions in total hip prosthesis. PATIENTS AND METHODS: CT was performed in 17 cases of suspected total hip prosthesis infection. Images were reviewed to evaluate for the presence of soft tissue abscess, hip joint effusion or fistula and peri-prosthetic lucency or erosion at bone window setting. The feasibility of CT imaging is assessed with regards to metallic artifacts. RESULTS: Infection was confirmed in 10 hips. A soft tissue abscess was present in 8 of these cases, in association to a joint effusion, presumably septic, in 7 cases. A fistula was identified in 8 cases. A peri-prosthetic lucency was present in 10 cases, 7 of which with infection, and erosions were noted in 4 patients, 2 of which with infection. Metallic artifacts reduced image quality but did not prevent detection of soft tissue abscesses. CONCLUSION: CT is useful for detection of soft tissue abscesses in patients with infected hip prosthesis. CT is useful for surgical planning or follow-up of patients treated conservatively.
Isolated non compaction of the left ventricle is a rare congenital cardiomyopathy linked to an arrest of normal myocardial embryogenesis. We report two cases of isolated non compaction of the left ventricle discovered by echocardiography in 2 males of 30 and 55 years. The first had progressively worsening cardiac insufficiency, the second was being followed for an unexplained cardiomyopathy. In both cases, the diagnosis was able to be confirmed by transthoracic echocardiography, supported by MRI data. Although present from birth, this condition can become apparent at various ages and is complicated by sudden death (principal cause of mortality), severe cardiac insufficiency, or thrombo-embolic accidents. The diagnosis of left ventricular non compaction should be considered when faced with unexplained cardiac insufficiency in the adult.
Sphenoid sinusitis is uncommon, with an incidence of about 2.7%. Failure to diagnose and treat sphenoid sinus disease has been shown to lead to serious neurologic sequellae. Plain radiographs play a limited role in the management of sinusitis. CT scan can provide a positive diagnosis by the visualization of mucosal thickening, air-fluid level and complete opacification of the sinusal cavities. In addition, CT can provide more information about the anatomy and abnormalities of the sphenoid sinus. MRI is used in cases of suspected tumors or neurologic involvement. The most common presenting symptom is headache that arise characteristically, but rarely, from the vertex. Sphenoiditis has a high risk of severe neurologic involvement, cavernous sinus thrombosis being one of the most serious complications.
Eukaryotic ribosome maturation depends on a set of well ordered processing steps. Here we describe the functional characterization of yeast Nog2p (Ynr053cp), a highly conserved nuclear protein. Nog2p contains a putative GTP-binding site, which is essential in vivo. Kinetic and steady-state measurements of the levels of pre-rRNAs in Nog2p-depleted cells showed a defect in 5.8S and 25S maturation and a concomitant increase in the levels of both 27SB(S) and 7S(S) precursors. We found Nog2p physically associated with large pre-60S complexes highly enriched in the 27SB and 7S rRNA precursors. These complexes contained, besides a subset of ribosomal proteins, at least two additional factors, Nog1p, another putative GTP-binding protein, and Rlp24p (Ylr009wp), which belongs to the Rpl24e family of archaeal and eukaryotic ribosomal proteins. In the absence of Nog2p, the pre-60S ribosomal complexes left the nucleolus, but were retained in the nucleoplasm. These results suggest that transient, possibly GTP-dependent association of Nog2p with the pre-ribosomes might trigger late rRNA maturation steps in ribosomal large subunit biogenesis.
Mitochondrial ribosomal proteins were studied best in yeast, where the small subunit was shown to contain about 35 proteins. Yet, genetic and biochemical studies identified only 14 proteins, half of which were predictable by sequence homology with prokaryotic ribosomal components of the small subunit. Using a recently described affinity purification technique and tagged versions of yeast Ykl155c and Mrp1, we isolated this mitochondrial ribosomal subunit and identified a total of 20 proteins, of which 12 are new. For a subset of the newly described ribosomal proteins, we showed that they are localized in mitochondria and are required for the respiratory competency of the yeast cells. This brings to 26 the total number of proteins described as components of the mitochondrial small ribosomal subunit. Remarkably, almost half of the previously and newly identified mitochondrial ribosomal components showed no similarity to any known ribosomal protein. Homologues could be found, however, in predicted protein sequences from Schizosaccharomyces pombe. In more distant species, putative homologues were detected for Ykl155c, which shares conserved motifs with uncharacterized proteins of higher eukaryotes including humans. Another newly identified ribosomal protein, Ygl129c, was previously shown to be a member of the DAP-3 family of mitochondrial apoptosis mediators.
The diagnosis of arterio-ureteric fistula must be considered in the case of sudden onset of abundant or intermittent haematuria occurring in a particular context (history of aorto-iliac vascular surgery, prolonged ureteric stenting, ilio-pelvic radiotherapy). Emergency treatment must control bleeding. Endovascular stenting may be a useful technique, followed by reconstructive surgery with vascular bypass graft and treatment of the ureteric lesion.
Ribonucleases III are double-stranded RNA (dsRNA) endonucleases required for the processing of a large number of prokaryotic and eukaryotic transcripts. Although the specificity of bacterial RNase III cleavage relies on antideterminants in the dsRNA, the molecular basis of eukaryotic RNase III specificity is unknown. All substrates of yeast RNase III (Rnt1p) are capped by terminal tetraloops showing the consensus AGNN and located within 13-16 bp to Rnt1p cleavage sites. We show that these tetraloops are essential for Rnt1p cleavage and that the distance to the tetraloop is the primary determinant of cleavage site selection. The presence of AGNN tetraloops also enhances Rnt1p binding, as shown by surface plasmon resonance monitoring and modification interference studies. These results define a paradigm of RNA loops and show that yeast RNase III behaves as a helical RNA ruler that recognizes these tetraloops and cleaves the dsRNA at a fixed distance to this RNA structure. These results also indicate that proteins belonging to the same class of RNA endonucleases require different structural elements for RNA cleavage.
The splicing process catalyzed by group II intron ribozymes follows the same two-step pathway as nuclear pre-mRNA splicing. In vivo, the first splicing step of wild-type introns is a transesterification reaction giving rise to a branched lariat intron-3'-exon intermediate characteristic of this splicing mode. In the wild-type introns, the ribozyme core and the substrate intron-exon junctions are carried by the same precursor molecule, making it difficult to distinguish between RNA folding and catalysis under normal splicing reactions. To characterize the catalytic step of the first transesterification reaction, we studied the reversal of this reaction, reverse branching. In this reverse reaction, the excised lariat intron and the substrate 5'-exon can be preincubated and folded separately, allowing the measure of the catalytic rate of the reaction. To measure the catalytic rate of the second splicing step, purified lariat intron-3'-exon intermediate molecules were preincubated and folded prior to the addition of 5'-exon. Conditions could be found where chemistry appeared rate limiting for both catalytic steps. Study of the metal ion requirements under these conditions resulted in the unexpected finding that, for the intron studied, substitution of magnesium ions by manganese ions enhanced the rate of the first transesterification reaction by two orders of magnitude but had virtually no effect on the second transesterification reaction or the 5' splice site cleavage by hydrolysis. Finally, the catalytic rates measured under optimal conditions for both splicing steps were faster by three orders of magnitude in the branching pathway than in the hydrolytic pathway.
During splicing of nuclear pre-mRNAs, the first step liberates the 5' exon (exon 1) and yields a lariat intron-3'exon (intron-exon 2) intermediate. The second step results in exon ligation. Previous results indicated that severe truncations of the 5' exon of the actin pre-mRNA result in a block to the second splicing step in vitro in yeast extracts, leading to an accumulation of intron-exon 2 lariat intermediates. We show that exogenous exon 1 RNA oligonucleotides can chase these stalled intermediates into lariat intron and spliced exons. This reaction requires some of the cis elements and trans-acting factors that are required for a normal second step. There is no strong sequence requirement for the exon 1 added in trans, but oligonucleotides with complementarity to the U5 snRNA conserved loop perform the chase more efficiently. Using a dominant negative mutant of the DEAH-box ATPase Prp16p and ATP depletion, we show that the stalled intermediate is blocked after the Prp16p-dependent step. These results show that exogenous RNAs with various sequences but containing no splicing signals can be incorporated into spliceosomes and undergo RNA recombination and exon shuffling during the second step of pre-mRNA splicing.
The variety of biogenesis pathways for small nucleolar RNAs (snoRNAs) reflects the diversity of their genomic organization. We have searched for yeast snoRNAs which are affected by the depletion of the yeast ortholog of bacterial RNase III, Rnt1. In a yeast strain inactivated for RNT1, almost half of the snoRNAs tested are depleted with significant accumulation of monocistronic or polycistronic precursors. snoRNAs from both major families of snoRNAs (C/D and H/ACA) are affected by RNT1 disruption. In vitro, recombinant Rnt1 specifically cleaves pre-snoRNA precursors in the absence of other factors, generating intermediates which require the action of other enzymes for processing to the mature snoRNA. Most Rnt1 cleavage sites fall within potentially double-stranded regions closed by tetraloops with a novel consensus sequence AGNN. These results demonstrate that biogenesis of a large number of snoRNAs from the two major families of snoRNAs requires a common RNA endonuclease and a putative conserved structural motif.
Small nucleolar RNAs (snoRNAs) are intron encoded or expressed from monocistronic independent transcription units, or, in the case of plants, from polycistronic clusters. We show that the snR190 and U14 snoRNAs from the yeast Saccharomyces cerevisiae are co-transcribed as a dicistronic precursor which is processed by the RNA endonuclease Rnt1, the yeast ortholog of bacterial RNase III. RNT1 disruption results in a dramatic decrease in the levels of mature U14 and snR190 and in accumulation of dicistronic snR190-U14 RNAs. Addition of recombinant Rnt1 to yeast extracts made from RNT1 disruptants induces the chase of dicistronic RNAs into mature snoRNAs, showing that dicistronic RNAs correspond to functional precursors stalled in the processing pathway. Rnt1 cleaves a dicistronic transcript in vitro in the absence of other factors, separating snR190 from U14. Thus, one of the functions of eukaryotic RNase III is, as for the bacterial enzyme, to liberate monocistronic RNAs from polycistronic transcripts.
Substrate sequences surrounding catalytic RNAs but not involved in specific, conserved interactions can severely interfere with in vitro ribozyme activity. Using model group II intron precursor transcripts with truncated or randomized exon sequences, we show that unspecific sequences within the 5' exon are particularly prone to inhibit both the forward and the reverse first splicing step (branching). Using in vitro selection, we selected efficient 5' exons for the reverse branching reaction. Precursor RNAs carrying these selected 5' exons reacted more homogeneously and faster than usual model precursor transcripts. This suggests that unfavorable structures induced by the 5' exon can introduce a folding step that limits the rate of in vitro self-splicing. These results stress how critical is the choice of the sequences retained or discarded when isolating folding domains from their natural sequence environments. Moreover, they suggest that exon sequences not involved in specific interactions are more evolutionarily constrained with respect to splicing than previously envisioned.
Thus far, conventional biophysical techniques, such as NMR spectroscopy or X-ray crystallography, allow the determination, at atomic resolution, of only structural domains of large RNA molecules such as group I introns. Determination of their overall spatial organization thus still relies on modeling. This requires that a relatively high number of tertiary interactions are defined in order to get sufficient topological constraints. Here, we report the use of a modification interference assay to identify structural elements involved in interdomain interactions. We used this technique, in a group II intron, to identify the elements involved in the interactions between domain V and the rest of the molecule. Domain V contains many of the active site components of these ribozymes. In addition to a previously identified 11 nucleotide motif involved in the binding of the domain V terminal GAAA tetraloop, a small number of elements were shown to be essential for domain V binding. In particular, we show that domain III is specifically required for the interaction with sequences encompassing the conserved 2 nucleotide bulge of domain V.